The present invention relates to a system and method of detecting when a subject is lying by conditioning the subject to produce a unique physiological response which is not a naturally occurring physiological phenomenon, in contrast to the prior methods which rely on monitoring natural responses. Specifically, using classical Pavlovian conditioning techniques and semantic generalization, a unique autonomic response is created in test subjects when they are exposed to a true versus a false statement (conditioned stimuli). This assures that an independent assessment can be made of whether a given examinee shows the conditioned response to known questions and allows quantitative comparisons of conditioned responses to the critical questions to be compared to the distribution of conditioned responses shown to known true and known false statements.
Current lie detection methods, based on the polygraph technique, rely upon detecting changes in the physiological characteristics of the subject. Among the characteristics measured are respiration rate, skin resistivity, blood pressure, and heart rate. One such method is the relevant/irrelevant test (RIT). As the name implies, the subject is asked a series of relevant and irrelevant questions. Measurements of the subject's physiological characteristics are made while the subject is answering these questions. If the physiological response to the relevant questions is greater than to the irrelevant questions, the subject is deemed to be deceptive. Responses of equivalent size to the two types of questions indicate truthfulness.
Another approach is the control question test (CQT). The CQT involves a comparison of responses to relevant questions, to certain control questions which are designed to elicit emotional reactions (e.g. “Have you ever taken something from someone who trusted you?”). Assuming that everyone has done the sorts of things asked in the control questions, innocent people should react more strongly to control questions than relevant questions. Conversely, dishonest people should react more strongly to relevant questions than control questions.
Yet another method is the Guilty Knowledge Test (GKT). In the GKT the subject is asked a series of multiple choice questions, all dealing with facts with which only those knowledgeable about the crime would be familiar. The GKT assumes that the guilty individual's recognition of the correct multiple choice alternative that contains actual details of the crime will lead to stronger physiological responses than to incorrect alternatives.
The technology used to monitor and record physiological measurements used by the polygrapher is typically a portable field polygraph. Recorded activity includes electrodermal responsitivity (for example skin resistance or conductance), monitored from stainless steel electrodes attached to the fingertips; respiration, recorded from pneumatic belts positioned around the upper chest and abdomen; and a “cardio” channel in which relative changes in blood pressure are determined by observing pressure oscillations obtained from a standard, partially inflated sphygmomanometer cuff placed on the subjects arm. Some methods may also record brain activity using electro-encephalography to measure P3 brain waves. Records are made either mechanically or are digitized and stored in a computer.
Even with control questions, the problem with all three of the methods described in previous paragraphs is that they rely on monitoring natural physiological responses which may fluctuate for reasons other than deceptive conduct or response to questions by the subject. Other potential problems and limitations are outlined in the National Research Council (2002) report on the scientific validity of the polygraph. Predictably, these methods produce false negatives (i.e. a deception is missed) and false alarms (subject is not lying, but inquisitor believes subject is). The problem of false positives and false negatives would be lessened if a novel autonomic pattern were semantically conditioned to true statements and the opposite novel autonomic pattern were semantically conditioned to false statements. These autonomic patterns would be involuntary, innocuous, and visibly undetectable, yet more accurate (i.e. lower false alarm rate) and sensitive (i.e. low false negative rate) than the traditional approaches described above.
Another problem with these traditional approaches is that they may be vulnerable to the deployment of countermeasures by the subject (National Research Council, 2002). Subjects who are aware that showing a stronger physiological response to control questions than to relevant questions is indicative of truthfulness can manipulate their physiology using cognitive, emotional, or motoric acts to influence their physiological responses to questions. One known countermeasure is increasing breathing by methods such as holding one's breath for 5–20 seconds after answering a control question. Another known countermeasure is to increase one's heart rate using methods such as constricting one's anal sphincter muscle, biting down on the tongue, or thinking exciting thoughts. Because of the effectiveness of such countermeasures, there is a need for a detectable response to lying that are more difficult to manipulate by the subject during testing.